Richard Knoppow (email@example.com)
Tue, 25 May 1999 00:47:43 -0700
There was an extended thread about this toner here recently. I finally
got a copy of the patent. For others interested it is USP 1,849,245, issued
March 15, 1932. The patent is assigned to Kodak but Ansco also published
the formula so it must have been cross-licensed somehow. I wonder what
Kodak got in return.
There is not much in the patent beyond the instructions given by Kodak
and Ansco but there are a couple of things of interest.
First, Nelson states that it is intended to be an improved version of the
Hypo-Alum sepia toner. He uses Ammonium Persulfate instead of alum (sodium
aluminum sulfate) but also states that he does not understand fully how the
persulfate works. He speculates that it has some sort of solvent action on
the silver particals which makes them more easily converted to sulfide. He
claims as advantages uniform color when toning multiple prints, predictable
and reproduceable results, no sediment on the prints, and freedom from
double toning when only partially toning a print.
The mixing instructions and use instructions are just about what is given
by both Kodak and Ansco.
Nelson also states "Toning baths containing hhypo and alum and also baths
in which gold chloride was combined with these constituents have been known
for many years..." but gives no references to any. I know of the use of a
separate gold toning bath to modify previously sepia toned prints but do
not know of any other hypo-alum type toners which also contain gold
chloride. If anyone out there does I would be glad to have a reference to it.
It is curious that his instructions say to return toned prints to the
fixing bath for five minutes. No rason is given for this. Kodak and Ansco
repeat this except that by the 1963 edition of Kodak's Processing Chemicals
and Formulas booklet this instruction has gotten lost. This is typical of
what happens when you get too far from original material.
This booklet has severely abreviated instructions for most of the
formulas given; I guess that by 1963 you were not expected to be mixing
your own stuff anymore.
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